code: def test_raises_error_if_evaluating_single_variable_and_threshold_is_None(
      df_test,
  ):
      X, y = df_test
  
      sel = SelectByTargetMeanPerformance(
          variables=["var_1"], threshold=None
      )
  
      with pytest.raises(ValueError):
          sel.fit(X, y)
  
file_path: feature_engine/tests/test_selection/test_target_mean_selection.py
imports: import pandas
  import pytest
  from feature_engine.selection import SelectByTargetMeanPerformance
label_desc: Use image node_id 6 for calling a global function with example usage: test_raises_error_if_evaluating_single_variable_and_threshold_is_None(df_test) without return types